Hydraulic servo-action system



March 17, 1959 A. BRUEDER 2,877,787

HYDRAULIC SERVO-ACTION SYSTEM Filed Fba 1, 1957 3 Sheets-Sheet 1 ZZBMarch 17, 1959 A. BRUEDER HYDRAULIC SERVO-ACTION SYSTEM 5 Sheets-Sheet 2Filed Feb. 1, 1957 T 'l fif.

United States atent HYDRAULIC SERVO-ACTION SYSTEM,

Antoine Brueder, Paris, France, assiguor to Soeiete Anonyme AndreCitroen, Paris, France Application February 1, 1957, Serial No. 637,772

Claims priority, application France September 14, 1956 2 Claims. (Cl.137-118) The present invention relates to improvements in or relating tohydraulic servo-action circuits of the type adapted to be associatedwith or incorporated in hydraulic systems, notably hydraulic suspensionsystems of automotive vehicles.

In a hydraulic servo-action installation or circuit it is necessary toprovide in conjunction. with the pump an accumulator for the fluid underpressure; therefore, meansmust be provided for controlling the pumpoutput to keep the accumulator pressure within predetermined limits andpermitting during the inoperative periods a zeropressure pump output.

An installation without accumulator may be contemplated if the pump iscapable of delivering the necessary instantaneous load output;nevertheless, an apparatus of generally delicate design is necessary forcontrolling the pressure.

In certain cases, circulation systems may be used and this solution isextremely simple when only one apparatus is to be actuated, but specialand costly arrangement must be provided when two or more receivers areused.

Now it is the essential object of this invention to provide a hydraulicservo-action system of the fluid-circulation type which comprises areservoir, a feed pump and two distributors each adapted to control theoperation of one receiver and to be controlled separately, thisarrangement being characterized in that a selector is interposed in thefeed circuit between the pump and the distributors for automaticallystopping the supply of fluid to the first distributor when the otherdistributor is operative and the first one is inoperative, and restoringthe supply of fluid to the first distributor if the latter is operatedwhereas the other distributor is already operative, the functions ofboth distributors being reversible.

With this purpose in view, the selector incorporated in the systemaccording to this invention comprises a body having formed therein aplurality of ducts, i. e. one inlet duct and two outlet ducts, thesethree ducts leading into a cylindrical cavity formed in said body andprovided with a distributing member of the slide valve type; the twoends of this slide valve are shouldered to a smaller diameter than thebore of said cavity and project in two side chambers each containing acalibrated compression spring urging the slide valve in its intermediateposition; moreover, a selection duct leads into each of these sidechambers.

Each distributor comprises essentially a body having formed therethrougha plurality of passages leading into a cylindrical axial cavity providedwith a distributor of the slide valve type; these passages constitutethe inlet, pump by-pass, selection, load. and exhaust ducts,respectively. Moreover, the distributor comprises a retarding passage ofgauged diameter interconnecting two cavities in which the two ends ofthe slide valve are slidably fitted.

The inlet, outlet and selection ducts are connected to the pump, and tothe corresponding inlet and selection ducts of the distributor. Finally,the pump by-pass duct provided in each distributor is connected to thefluid reservoir.

In order to afford a clearer understanding of the present invention andof the manner in which. the same may be carried out in the practice,reference will now be made to the accompanying drawings forming partofthis specification and illustrating diagrammatically by way of ex:-ample a typical embodiment of the invention. In the drawings:

Figure 1 is a diagram illustrating the hydraulic servoaction systemaccording to this invention, the diiferent component members thereofbeing shown in their inoperative positions.

Figure la is a diagram showing a distributor in its operative position.

Figure 2 is a longitudinal section taken along the axis of adistributor.

Figure 3 is a cross-section taken upon the line III--III of Fig. 2.

Figures 4, 5, 6 and 7 are simplified, fragmentary cross sectionsillustrating the positions of the different ducts, the sections beingtaken upon the lines IV--IV, V-V, Vl-Vl and VII-VII of Fig. 2.

Figure 8 is a plan view of a distributor, and

Figure 9 is a longitudinal section illustrating the selectorarrangement.

In Fig. l, which constitutes a condensed, diagrammatic view of ahydraulic servo-action system according to this invention, a pump P isconnected to a fluid reservoir R through a pipe line 1 and to a selectordevice S through another pipe line 2 in which a safety valve 3 may beinterposed, if desired. The outlet ducts of selector S are respectivelyconnected through other pipe lines 4, 5 to the inlet ducts ofdistributors D and D the delivery ports 26A and 26B of thesedistributors being connected through corresponding pipe lines 39, 40respectively to two receivers 41 and 42.

The selector S (Fig. 9) comprises a. body 6 in which.

a cylindrical bore 7 adapted to receive a slide-valve distributor 8 isformed. This valve comprises two end portions 8a, 8b of a diametersmaller than that of the bore 7, two portions 80, 8d of same diameter asthe bore 7, and an intermediate portion 8ev of same diameter as the endportions 812, 812. An inlet duct 9 connected through the pipe line 2 tothe pump P leads into the bore 7 and its axis is coincident with thecentral trans verse plane of this bore, as shown. Other ducts 10 and 11connected through the pipe lines 4 and 5 to the inlet ducts ofdistributors D and D respectively lead into the intermediate portion ofthe cavity 7. Each duct 10, 11 is chambered and adapted to receive aball 10a, 11:: acting as a non-return valve as will be made clearpresently. The end portions 8a, 8b of the slide valve emerge in chambers12 and 13 respectively. Calibrated springs 14, 35 hearing against theouter bottoms of these chambers tend to keep the slide valve 8 in itscentral or intermediate position as shown in Fig. 9 by engaging discs16, 17 bearing on the outer faces of portions and 8d of the slide valve,respectively. The chambers 12, 13 communicate with selection ducts l8,19 respectively, and the latter are connected through pipe lines 20, 21(Fig. l) to the selection ducts of distributors D and D respectively- Asillustrated in Fig. 9, the safety valve 3 may be. mounted on the. body 6instead of being inserted in the line leading from the pump P.

The distributors D and D are identical and their in ternal structurewill now be described with reference to Figs. 2 to 8.

The distributor comprises essentially a body 22 havi ng.

gowns":

formed therein an axial cylindrical cavity 23 in which a slide valve 24is slidably mounted, as shown. This slide valve 24 comprises two endportions 24a, 24b and two intermediate portions 24c, 24d all of whichhave a smaller diameter than the bore of the cavity 23, and threeportions 24e, 24f, 24g of same diameter as the aforesaid bore. A numberof ducts lead into or from the cavity 23, i. e. the exhaust duct 25(Fig. 3), the load duct 26 connected to the receiver, the selection duct27 connected to the corresponding pipe line 20 or 21 (Fig. and the pumpby-pass duct 28 leading to the reservoir R (Fig. 6). The inlet duct 29communicates with the cavity 23 through an annular channel 30 and a duct31 (Fig. 7) and through a longitudinal channel 32 and an annular channel33 with the selection duct 27 in the inoperative position of the slidevalve 24 (Fig. 1), and also with the axial cavity 23 through the duct31a (Fig. 5). The distributor body has also formed therein a duct 34 ofgauged diameter for interconnecting the end chambers 35 and 36. Thepurpose of this duct 34 is to retard the circulation of fluid betweenthese chambers 35 and 36 when the slide valve 24 is moved within thebore 23 by adequate means (not shown).

The operation of the hydraulic servo-action system according to thisinvention will now be described with reference to the diagram of Fig. 1.

The receivers 41 and 42 fed with fluid through the distributors D and Dmay constitute, as shown diagrammatically in Fig. 1, the front and rearcorrectors respecti vely of a hydraulic or hydro-pneumatic suspensionsystem of a vehicle. These correctors are designed to modify the levelof the suspension as a function of the load so as to keep this level toa constant value.

' Under normal conditions the different slide valves 8 of the selectorS, 24a of distributor D and 24b of distributor D are in theirinoperative positions as illustrated in Fig. 1. Thus, the fluidcirculates normally through the following circuit, in the case of thedistributor D,: reservoir R, pipe line 1, pump P, pipe line 2, cavity 7,valve a, duct 10, pipe line 4, duct 29 (Fig. 7), channel 30, duct 31,axial cavity 23, duct 28, return pipe line 37. Through the channel 32,annular channel 33, duct 27 and pipe line 21, the chamber 13 of selectorS is then at low pressure. A similar circuit is established through thepipe line 5, distributor D and return pipe line 38; the pressure in thechamber 12 of selector S is the same as in chamber 13. If thedistributor D is actuated, that is, if the slide valve 24a is moved tothe lefthand side of Fig. 1 (for example to correct the rear suspension)the circuit passing through the distributor D will be established asfollows (Fig. 1a): inlet duct 29, annular channel 30, channel 32, cavity23 and load duct 26. Under these conditions, the fluid pressureincreases to overcome the resistance of the load device or receiver.However, if the selector device S were not provided, the fluid pressurecould not rise due to the low-resistance circuit remaining open throughthe distributor D as the latter is not actuated. Now, as the piston 24awas moved to the left the pump by-pass duct 28 was thus closed, thepressure in the cavity 23 rises instantaneously due to the resistanceoffered by the receiver 41 thus inserted in the circuit. This briefincrease in the hydraulic pressure is transmitted immediately throughthe pipe line 21 to the chamber 13 of selector S; as a result, the slidevalve 8 is moved quickly to the left and its portion 8d closes the duct11. Consequently, the supply of fluid to the distributor D isdiscontinued and the pressure may continue to rise in the load duct 26and the receiver may be actuated, until the slide valve 24a resumes itsinoperative position. This operation may be comprised by the incompleteclosing of the duct 31a which would permit an escape of fluid underno-pressure conditions through the circuit 32, 30, 31, 29, 4, 7, and 5and distributor D now in its exhaust position; thus, the ball valve 10ainserted in the duct 4 will close the passage and enable the fluidpressure to be set up in the aforesaid circuit and therefore also in theelements 27, 21 and chamber 13; consequently, the piston 8 is forced tothe left and the distributor D isolated from the operative circuit. Asthe fluid under pressure delivered from the pump P cannot flow directlytowards D the pressure rises in the cavity 7 and may be transmittedthrough the pipe line 4 and the other distributor D to the receiver tobe actuated. The fluid from the pump may flow without difficulty bylifting the previously seated ball valve 10a. As the slide valve resumesits inoperative position, the pressure in the pipe line 21, andtherefore in chamber 13, drops to the initial value due to thecommunication established with the reservoir R through the followingcircuit: duct 27, annular channel 33, channel 32, duct 31, cavity 23,duct 28, pipe line 37. Thus, the slide valve 8 of selector S resumes itsinitial or inoperative position.

The distributor D operates in a similar manner.

Let us assume that the distributor D is already operated, so that itsslide valve 24a is moved to the left, and that under these conditionsthe other distributor D; is also actuated. In this case the slide valve8 of selector S has already been moved to the left and the pipe line 5is not fed from the pump P. Consequently, the movement of theslide-valve portion 24b to the left causes the load duct 26b tocommunicate with the selection duct 27b. The counter-pressure exerted bythe load device or receiver is transmitted through the pipe line 20 tothe chamber '12 of selector S. This counter-pressure acts upon the end811 of slide valve 8 to restore the latter in its inoperative positionin which both distributors D D are fed with fluid under pressure. Thefluid circulating in the pipe line 5 is then transmitted through thedistributor D the load duct 26b and the pipe line 40 to the receiver 42controlled by the distributor D The rapidity of the return movement ofthe slide valve 8 depends at the same time on the pressure drops in theinstallation, on the calibration of the various springs therein and onthe pressure differential between the pump and the load or like devicesassociated with and controlled by this installation. In all cases, thecorrection times may be adjusted to be very short and the two actionsmay take place in succession without any inconvenience.

Although the attached drawings and the above description refer to onlyone typical embodiment of the inven tion, it will be readily understoodby anybody conversant with the art that many modifications andalterations may be brought thereto without departing from the spirit andscope of the invention, as set forth in the appended claims.

What I claim is:

l. A hydraulic servo-action system with fluid circulation, comprising areservoir, a pump connected to said reservoir, a first distributor and asecond distributor connected in parallel to the delivery side of saidpump, each of said distributors comprising a cylindrical body, an axialcavity formed therethrough, a distributor valve slidably movable in saidcavity, a pump by-pass duct connected to said reservoir, an exhaustduct, an inlet duct, a selection duct, a load duct, all these ductsbeing disposed radially and leading into said axial cavity, a firstreceiver and a second receiver connected to the load ducts of the firstdistributor and second distributor respectively, a selection membercomprising a body, a cylindrical cavity formed therethrough, an inletduct connected to said pump, a first outlet duct and a second outletduct connected to the inlet ducts of said first and second distributorsrespectively, a non-return valve inserted in each of said outlet duets,said outlet ducts being formed in said body and leading into saidcylindrical cavity of said selector, a slide valve movable within saidselector cavity, two widened side chambers in which the two end portionsof said slide valve project, a calibrated spring in each of saidchambers for keeping said selector slide valve in its intermediateposition by acting on said projecting end portions, a first selectionduct and a second selection duct leading into each of said chambers,respectively, and connected to the selection ducts of said firstdistributor and second distributor, respectively, the pressure increaseoccurring in the selection duct of the first distributor when the latteris actuated to feed the first receiver being transmitted to the firstselection duct of the selector and producing a movement of the selectorslide valve to control the closing of the second outlet duct of theselector which is connected to the inlet duct of the second distributor,the counter-pressure produced subsequently in the selection duct of thesecond distributor when the latter is controlled to feed the secondreceiver while the first receiver is already fed being transmitted inthis case to the first selection duct of the selector and causing theslide valve to resume its intermediate position, the opening of thesecond outlet duct, and therefore, the supply of fluid to the seconddistributor.

2. A hydraulic servo-action system with fluid circulation, comprising areservoir, a pump connected to said reservoir, 21 first distributor anda second distributor connected in parallel to the delivery side of saidpump, each of said distributors comprising a cylindrical body, an axialcavity formed therethrough, a distributor valve slidably movable in saidcavity, a pump by-pass duct connected to said reservoir, an exhaustduct, an inlet duct, a selection duct, a load duct, all these ductsbeing disposed radially and leading into said axial cavity, a firstreceiver and a second receiver connected to the load ducts of the firstdistributor and second distributor respectively, a selection membercomprising a body, a cylindrical cavity formed therethrough, an inletduct connected to said pump, a first outlet duct and a second outletduct connected to the inlet ducts of said first and second distributorsrespectively, said outlet ducts being formed in said body and leadinginto said cylindrical cavity of said selector, a slide valve movableWithin said selector cavity, two widened side chambers in which the twoend portions of said slide valve project, a calibrated spring in each ofsaid chambers for keeping said selector slide valve in its intermediateposition by acting on said pro jecting end portions, a first selectionduct and a second selection duct leading into each of said chambers,respectively, and connected to the selection ducts of said firstdistributor and second distributor respectively, the pressure increaseoccurring in the selection duct of the first distributor when the latteris actuated to feed the first receiver being transmitted to the firstselection duct of the selector and producing a movement of the selectorslide valve to control the closing of the second outlet duct of theselector which is connected to the inlet duct of the second distributor,the counter-pressure produced subsequently in the selection duct of thesecond distributor when the latter is controlled to feed the secondreceiver While the first receiver is already fed being transmitted inthis case to the first selection duct of the selector and causing theslide valve to resume its intermediate position, the opening of thesecond outlet duct, and therefore, the supply of fluid to the seconddistributor.

References Cited in the file of this patent UNITED STATES PATENTS1,999,834 Ernst Apr. 30, 1935 2,624,361 Brown Jan. 6, 1953 2,799,996 VanMeter July 23, 1957

